## Host REST API with Express: Stored Input and Output Artifacts

### Summary  
Deploy a REST API built with Express on Ample using the generated downloads pattern. Compute runs the app in an isolated microVM behind a public HTTPS URL, a managed PostgreSQL 16 database is auto-provisioned and injected as DATABASE_URL, a private S3-compatible bucket holds objects with credentials delivered as encrypted environment variables. Verified on Express: an export query rendered to a CSV artifact stored with metadata in a private bucket and returned only to an authorized caller (401 without token, export=ok rows=3). Not separately tested: your export formats, retention policy and entitlement model; treat the REST API-specific behavior as your application code.

### Representative Queries  
- Host REST API with Express: stored input and output artifacts  
- Where can I host REST API built with Express?  
- I need an input/output artifact contract, object metadata and access boundaries.

### Resource Requirements  
- primitive:compute  
- primitive:postgres  
- primitive:s3-compatible-object-storage

### Infrastructure Requirements  
- **Compute**  
  Apps run in isolated x86_64 Firecracker microVMs that auto-pause when idle and wake on request; sizes are the priced VM sizes.  
  Status: verified  
  Summary: isolated microVMs

- **Postgres**  
  Managed PostgreSQL 16 runs in its own microVM and is auto-provisioned when an app needs a database and no DATABASE_URL is supplied.  
  Status: verified

- **S3-compatible object storage**  
  Buckets are S3-compatible with issued credentials; PutObject and GetObject are verified by canary. Other S3 operations are not verified.  
  Status: verified

### Workflow Steps  
1. **Build and Start**  
   npm install, npm run build --if-present, npm run start on the node-22 template. The server must bind 0.0.0.0 on PORT.

2. **Implement the Pattern on PostgreSQL**  
   The fixture's module implements generated downloads: an export query rendered to a CSV artifact stored with metadata in a private bucket and returned only to an authorized caller (401 without token, export=ok rows=3). Copy the approach into your schema; keep migrations idempotent and run them with --release-command.

3. **Wire Object Storage**  
   Create the bucket(s), then pass endpoint, region, bucket and keys as --env values. Use path-style addressing. Keep private data in an unpublished bucket.

4. **Deploy**  
   Run the synchronous deploy once and read the result (exit 0 live, 1 failed, 2 blocked). Re-running with no change is a no-op.
   
   Command: `ample deploy . --name  --public --env S3_ENDPOINT=... --env S3_REGION=... --env S3_BUCKET=... --env S3_ACCESS_KEY_ID=... --env S3_SECRET_ACCESS_KEY=...`

5. **Verify**  
   Fetch the live URL and the pattern self-test route(s) (/p/generated-downloads) from the example; then run your own checks. On failure read `ample logs  --kind build` then `--kind runtime`.  
   Command: `ample logs  --kind build`

### Examples  
- **Express Pattern Fixture**  
  Multi-pattern Express app whose generated downloads module was checked live; the module is under tests/deploy-canaries/_pattern-modules.

### Success Checks  
- App responds on its public URL  
  Kind: http_get  
  Path: /  
  Expect: ample canary express patterns

- Generated downloads self-test  
  Kind: http_get  
  Path: /p/generated-downloads  
  Expect: export=ok rows=3 (with ?token=...; 401 without)

### Limitations  
- Verified on the node-22 template at s-1vcpu-1gb with the example fixture; other sizes, templates and Express major versions are not verified.  
- The REST API itself (your export formats, retention policy and entitlement model) is application code and was not separately tested; the pattern checks are what was verified.  
- Region, compliance attestations and request-duration limits are unknown and not claimed.  
- Apps auto-pause when idle and wake on the next request; always-on is an operator setting, not a plan feature.  
- Managed PostgreSQL 16 only; extensions, connection limits and backup or restore procedures are not verified; apps and their databases are placed together.  
- PutObject and GetObject with path-style addressing are verified; multipart upload, listing, presigned URLs and lifecycle rules are not verified.

### Cost Estimate  
- **Currency:** USD  
- **Monthly Amount:** $10.00  
- **Basis:** size prices from pricing.toml (loaded by the API) at build revision 1ac5595375130d45290090e82ed0f554ccd45405-dirty  
  - Components:  
    - App server: s-1vcpu-1gb, Quantity: 1.0, Monthly Amount: $5.00  
    - Managed PostgreSQL database: s-1vcpu-1gb, Quantity: 1.0, Monthly Amount: $5.00  
- Note: Always-on monthly price of the tested sizes; apps and databases auto-pause when idle. Buckets are allocation-priced per quota and not included.